1. Field of the Invention
This invention relates to the manufacture of reinforced catheters, tracheal tubes, tracheotomy tubes and other medico-surgical tubes and to the resulting products. More particularly, it concerns the production of medico-surgical tubes that have a central body portion containing a helix of a rigid plastic filament that serves to strengthen the tubes so as to resist kinking and collapsing during use.
2. Description of the Prior Art
This invention relates to uncuffed and balloon-type catheters, i.e., catheters which may be provided at the distal end with an inflatable balloon or cuff which serves, during the medical or surgical procedure performed using the catheter, to retain the catheter in a desired position within the patient, to seal a passage in the patient, etc.
Medico-surgical tubes may assume a variety of sizes, shapes and be provided with a variety of fluid openings, couplings, connectors or the like. Terminology applied to such devices by users, e.g., physicians, surgeons, hospitals, etc., frequently refer to them as catheters, e.g., rectal catheters, urethral catheters, hemostatic catheters and the like, but in other cases they are referred to as tubes, e.g., endotracheal tubes, feeding tubes, suction tubes, drain tubes and the like. For the sake of brevity in describing the improved devices of the invention and their method of production, the term "catheter" is employed throughout the specification and accompanying claims to encompass pertinent medicosurgical devices whether they be popularly referred to by the medical profession and other users as "catheters" or "tubes."
Many forms of medico-surgical tubes that comprise a lumen through which fluids may be passed to or from the body of a patient are known. The simplest of these are the catheters (see U.S. Pat. Nos. 2,437,542; 2,857,915; 3,485,234; 3,605,750; 3,618,613; and 4,210,478). More complex medico-surgical tubes include endotracheal tubes (see U.S. Pat. Nos. 3,625 793; 3,684,605; 3,725,522 and 3,755,525), post surgical tubes (see U.S. Pat. No. 3,589,368), tracheotomy tubes (see U.S. Pat. No. 3,973,569), sump drain tubes (see U.S. Pat. No. 3,314,430) tubes for urological use (see U.S. Pat. No. 2,268,321) and esophogeal endoprosthesis tubes. The present invention provides an improved medico-surgical tube and a method for the production thereof, the medico-surgical tube having a novel distal end.
It is desirable with most types of medico-surgical tubes that they be flexible and have as thin a wall as possible. There is a trade-off, however, in constructing the medico-surgical tube with thin walls and high flexibility, i.e., the thinner and more flexible the tube, the greater the possibility the tube will kink or collapse during use. Since kinking or collapsing can result in complete closure of the lumen with attendant damage or death to the patient, medico-surgical tubes must be structured so as to mitigate kinking.
One way the industry has developed to provide medico-surgical tubes with increased strength but not necessarily with low kinking potential is to include in them a braided wire sheathing embedded between plastic layers (see Great Britain Patent Publication No. GB 2043201A) or a helix of metal wire or synthetic filament (see Canadian Patent No. 1,199,761). Such helix containing tubes are referred to in the trade as "reinforced." In the reinforced tubes, the spacings between coils of the helix are quite small, e.g., 1-3 mm, and are to be contrasted to catheters and like tubes comprising filaments to increase tensile or burst strength, rather than compressive strength (see U.S. Pat. No. 2,268,321). The distal end of the catheter shown in FIGS. 11-13 of U.S. Pat. No. 2,268,321 is not reinforced by a filament helix such that a plurality of coils of the filament helix is provided in the distal end.
Metal wire reinforced tubes, however, are disadvantageous in that they will not spring back when partially collapsed. For instance, if a patient bites down on a metal wire reinforced tracheal tube, the metal wire would be deformed beyond its elastic limit such that the tube remains in a collapsed condition. Such collapsing of the tube can result in nearly complete closure of the lumen with attendant hazard to the patient. Filament reinforced tubes, on the other hand, are more resistant to kinking and crushing because they can spring back when collapsed.
Various methods are known in the art for producing a distal end on such medico-surgical tubes. For instance, a continuous, extruded tube can be square-cut at the proximal end and have a bevel or angle-cut at the distal end. In pure plastic without reinforcing this cutting is straight forward. Subsequent finishing of the distal end can be accomplished by pushing the angle cut end into a heated mold that melts the PVC and forms it into the shape of the mold (see U.S. Pat. No. 3,725,522 and Canadian Patent No. 1,199,761). With this technique, the square edges of the angle cut tip can be made smooth and radiused. An eye can be punched through the long part of the distal end. This can be accomplished by placing a flat mandrel inside the tube and driving a cookie-cutter type punch through the wall.
For extruded tracheal tubes reinforced with wire, however, complicated, and therefore costly end finishing methods have heretofore been used. (See GB 2043201A and Canadian Patent No. 1,199,761). For instance, distal end finishing methods for reinforced tubes include placing a square-cut end into an injection mold, forming the complete tip purely of plastic and at the same time fusing it to the reinforced tube. Alternatively, a pure plastic (wire-free) tip can be made by separately extruding pure plastic tubing of identical ID and OD to the reinforced tube and the tip can be secured to the tube section with solvent or glue. Another method involves stripping of the wire out from between the tube inner and outer walls of a simple square-cut distal tip and the two walls can be welded together with glue after which the tip is then angle-cut, heat-mold finished, and eye punched. It may also be possible to provide spaced, helix or sheathing free portions (such as by intermittently stopping the coiling of filament or sheathing about a base tube) and the tube can be cut to form distal ends of the tube in the helix-free portions of the tube.
A prior art catheter 1 shown in FIG. 1 comprises a molded, helix-free distal end 2, a molded, helix-free proximal end 3 and central body portion 4 containing a helix 5 (see FIG. 2). In order to safeguard against the possibility of the distal end of the helix 5 (particularly where it is made of metal wire) penetrating the outer layer of the catheter 1 during its use, a small loop 6 (see FIG. 3) is formed in the distal end of helix 5 prior to forming the molded distal end 2 on the catheter 1. A rigid molded connector 7 has its distal end 8 encircled by a slightly expanded proximal end 3 of the catheter 1.
Prior to the present invention, the production of distal ends of reinforced medico-surgical tubes has been a labor intensive operation (see Canadian Patent No. 1199761 and GB 2043201A). Furthermore, such distal ends have heretofore been provided without reinforcement for increasing compressive strength of the distal ends. The present invention concerns improved methods for production of distal ends of rigid plastic filament reinforced medico-surgical tubes at lower costs and higher degree of uniformity of product than has been possible heretofore.